1. Field of the Invention
The present invention relates to an image forming apparatus provided with a sheet conveying direction switching mechanism for switching a conveying direction of a sheet being conveyed.
2. Description of the Related Art
Conventionally, there has been known a sheet conveying direction switching device used in a sheet conveyor system of an image forming apparatus. For example, a device for switching a conveyance destination of a sheet having a toner image formed on a surface upon the completion of an image forming process between a discharge tray and a switchback conveyance path for a two-sided printing process is known as such a sheet conveying direction switching device. Such a sheet conveying direction switching device includes a rotary guide member disposed at a diverging point to discharge destinations for switching the conveyance destination of the sheet.
This rotary guide member is composed of a pair of circular side plates arranged to face at a distance slightly longer than the width of the sheet, four guide plates extending between these circular side plates and rotary shafts each projecting from the corresponding circular side plate. The rotary guide member is rotatable about the rotary shafts. Different guide paths (straight guide path in the center and reversing guide paths at the opposite sides) are defined between the respective guide plates. Which of the guide paths the sheet conveyed to the rotary guide member passes is determined based on a rotation amount from a reference phase (rotational position as a reference) of the rotary guide member. According to the guide path along which the sheet passes, the sheet is discharged to the preset conveyance destination.
Such a rotary guide member is driven and rotated about the rotary shafts by a stepping motor which is driven and rotated according to a pulse number of a pulse signal. In this way, the posture of the rotary guide member is set (i.e. the conveyance destination of the sheet being conveyed is set).
The stepping motor rotates only by an angle corresponding to the pulse number of the pulse signal from the present position. Thus, the rotary guide member is first set in a preset reference posture and, in this state where the rotary guide member is set in the reference posture, the stepping motor is rotated, for example, by a pulse signal having a pulse number corresponding to the discharge tray or by a pulse signal having a pulse number corresponding to a switchback conveyance path, whereby the rotary guide member can be set (positioned) in the reference posture (rotational position) determined beforehand according to the conveyance destination. Thus, the image forming apparatus of this type normally includes a reference posture detection sensor for detecting that the rotary guide member has reached the reference posture in order to position the rotary guide member in the reference posture.
On the other hand, there has been conventionally provided no means (sensor) for directly detecting an abnormality of the motor for driving the rotary guide member. Thus, an abnormality is indirectly judged to have occurred in the motor if the rotary guide member was not rotated and no detection signal was output from the reference posture detection sensor even through an instruction was given to drive and rotate the rotary guide member.
In this way, the abnormality of the motor was judged when the rotary guide member was not rotated. Thus, an abnormally was judged to have occurred in the stepping motor and a notification was given to inform the abnormality of the stepping motor and prompt an inspection request to a service person not only when the abnormality occurred in the stepping motor itself, but also when the rotation of the rotary guide member was hindered, for example, by a mere sheet jam.
However, there are causes of abnormalities that can be dealt with by a user himself without requiring the service person to inspect. One example is a case where the rotation of the rotary guide member is hindered by a sheet jam. If the user contacts the service person and lets him to deal with a problem although this problem can be dealt with by the user himself, it increases burdens on a party in charge of apparatus maintenance and is not also preferable to the user since the user cannot use the image forming apparatus until a problem solving operation by the service person is completed.